I took a bit of plastic from the remains of my dipstick housing (part of it fell into the oil pan) and held it in a spoon, which I held over a Zippo burning “light petroleum distillate”. The spoon was hot enough to boil water when I plunged it into the cup. The bit of plastic melted in the spoon, so without knowing the spoon temperature, I can’t say for sure if I'm risking melted plastic in my oil pan. Any of you have a ballpark guess for the temperature lighter fluid burns at?